Liquid crystal with alternating protrusions and grooves separating pixel electrodes

ABSTRACT

A liquid crystal on silicon (LCOS) panel in single-domain vertical alignment mode. The LCOS includes a front plate, a rear plate, and a liquid crystal layer. The rear plate includes a number of pixel electrodes and the pixel electrodes are grouped in pairs. Every two pairs of pixel electrodes are separated by a groove while the pixel electrodes in each pair are separated by a protrusion. The LCOS panel is filled with the liquid crystal layer, between the front and rear plates, while the liquid crystal molecules in the liquid crystal layer are in vertical alignment mode. By the configuration of the protrusions and grooves among the pixels of the LCOS panel, a single domain is readily formed in every pixel while high contrast ratio, reduced fringe field effect and effect of transverse electric field can be achieved.

This is a continuation of application Ser. No. 10/127,413, filed Apr.23, 2002, now U.S. Pat. No. 6,665,041.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a liquid crystal on silicon (LCOS),and more particularly to a vertical alignment (VA) mode liquid crystalon silicon capable of forming a single domain.

2. Description of the Related Art

As the market of portable products, e.g., personal digital assistant(PDA), cellular phone, and projector, and large-sized projectiontelevision progress, more and more customers require that theresolutions of these portable products or the projection television areto be identical to that of personal computer systems. Liquid crystal onsilicon (LCOS) is just enough to fulfil these requirements. Unlikeliquid crystal display (LCD) whose the front and rear plates are made ofglass, LCOS employs a silicon plate and glass plate between which liquidcrystal is filled. The structure of LCOS can provide displays not onlymeeting the requirement for compactness of portable products, but alsohaving high resolution. The resolution of a display is represented bypixels formed on the plates. The more the pixels a display has, thefiner and the resolution the display can show. In addition, LCOS iscapable of having its driving circuit manufactured by usingsemiconductor manufacturing process, e.g., complementary metal oxidesemiconductor manufacturing process so that the silicon plate that usessilicon wafer can be manufactured in a standard semiconductormanufacturing production line. Therefore, it is unnecessary to investadditionally in the production equipment while the resolution of theLCOS is higher than that of the LCD, which requires glass-manufacturingprocess.

Liquid crystal on silicon can be categorized into transmissive type andreflective type while major research and development focus on thereflective type. FIG. 1A shows a single pixel on a reflective-type LCOSin a cross-sectional view. The LCOS has a front plate 100 and a rearplate 101. The rear plate 101 includes a silicon substrate 102 on whicha thin film transistor 106, an opaque layer 107, and a capacitor 108 areformed. The thin film transistor 106 is used for controlling theoperation of the pixel, the opaque layer 107 is used for making the thinfilm transistor 106 from not being shined so as to avoid misoperation,and the capacitor 108 is used for maintaining the brightness of thepixel. A metal layer 111 is electrically coupled to the thin filmtransistor 106 and the capacitor 108 while the metal layer 111 iscovered with an insulating layer 109. In addition, a pixel electrode 110is disposed above the insulating layer 109 and is covered with areflector 112. As to the front plate 100, a glass plate 120 is includedand a transparent electrode (indium-tin-oxide electrode) 118 is formedon the glass plate 120. The front plate 100 and the rear plate 101 areassembled in parallel and the space between them is filled with liquidcrystal molecules 115 so as to form a liquid crystal layer 114. Further,alignment films 113 and 116 for molecular alignment are formed on thereflector 112 and the transparent electrode 118.

By the above structure, a light signal having brightness correspondingto a voltage applied to the pixel electrode 110 is obtained. When anincident ray (denoted by I, as shown in FIG. 1A) that is normal to theliquid crystal layer 114 strikes the glass plate 120, a reflected ray(denoted by O) is reflected by the reflector 112. The polarization ofthe light passing through the liquid crystal layer 114 is modulated bychanging the alignment of the liquid crystal molecules 115 that isvarying with a voltage applied to the pixel electrode 110. After that,the reflected ray is processed by the polarizing film (not shown in FIG.1A) formed on the glass plate 120. In this way, the polarized reflectedray has the brightness corresponding to the voltage applied to the pixelelectrode 110.

FIG. 1B illustrating an LCOS in a top view. As shown, each of the pixelelectrodes 110 is isolated with grooves 124, wherein the bottoms of thegrooves 124 are covered with the alignment film 113.

To be more specific, when a voltage is applied to the pixel electrodes110, the arrangement of the liquid crystal molecules is to be varied sothat the light transmission changes. Thus, the LCOS can display imageswith different brightness such as white, black, and intermediate grayscale. In addition, the molecules of the liquid crystal layer of LCOSpanels can be categorized into twisted nematic mode (TN) and verticalalignment mode (VA). FIGS. 2A–2B show the operations of liquid crystalmolecules in twisted nematic mode when a voltage is not applied orapplied to the liquid crystal molecules, respectively. When an electricfield is not applied across the alignment films 202 and 204, the liquidcrystal molecules 200 gradually twist layer by layer until the uppermostlayer is at a 90° angle to the bottom layer, as shown in FIG. 2A. When asufficient electric field is applied, the liquid crystal molecules 200are to be aligned and parallel to the direction of the electric field,as shown in FIG. 2B. FIGS. 3A–3B show the operations of liquid crystalmolecules in vertical alignment mode when a voltage is not applied or isapplied to the liquid crystal molecules, respectively. When a voltage isnot applied across the alignment films 302 and 304, the liquid crystalmolecules 300 are aligned and perpendicular to the alignment films 302and 304, as shown in FIG. 3A. When a voltage is applied, the liquidcrystal molecules 300, as shown in FIG. 3B, are to be twisted by anangle of 90° to the direction of the liquid crystal molecules 300 whenthe voltage is not applied, while they are parallel to the alignmentfilms 302 and 304.

As compared with LCOS panels with liquid crystal molecules in twistednematic mode, LCOS panels with liquid crystal molecules in verticalalignment mode have higher contrast ratios. A twisted nematic LCOS panelcan provide a contrast ratio of about 100:1 to 150:1, but avertical-alignment LCOS panel can provide a contrast ratio of about400:1 or above. Therefore, the development of LCOS panels with liquidcrystal molecules in vertical alignment mode is interested.

Moreover, the liquid crystal layer 114 can be damaged if a voltage inthe same polarity is continuously applied to the pixel electrode 110.This problem can be avoided by using polarity inversion because the graylevels produced by the LCOS panel is related to the difference betweenvoltages across the liquid crystal layer 114 but not related to thepolarities of the voltages. Polarity inversion is a driving method thata voltage of alternate positive and negative is applied to the pixelelectrode 110. With respect to polarity inversion, liquid crystaldisplay driving methods can be categorized into frame inversion, columninversion, and dot inversion. The following is to describe the threedriving methods briefly.

FIG. 4A illustrates the conventional frame inversion driving method fora liquid crystal display (LCD) panel 400 having a number of pixels 401.The positive sign “+” and negative sign “−”, hereinafter, are indicativeof polarities of the voltages applied to the associated pixels. In frameinversion, if positive voltages are applied to all pixels at one time,then negative voltages are applied to them in the next time instant. Inthis way, voltages in positive and negative polarities are alternatelyapplied to them.

FIG. 4B illustrates the conventional column inversion driving method foran LCD panel 402 having a number of pixels 403. In column inversion,polarity inversion occurs on pixels of columns. If positive voltages areapplied to a column of pixels, negative voltages are applied to theadjacent column of pixels. In the next time instant, the polarities ofvoltages applied to the above pixels are inverted. That is, negativevoltages are applied to the column of pixels that the positive voltageshave been applied to, while positive voltages are applied to theadjacent column of pixels that the negative voltages have been appliedto. In this way, the application of voltages in positive and negativepolarities to the other columns of pixels changes. In this example, theunit that polarity inversion occurs on is one column of pixels.Naturally, this unit can be extended. For instance, two columns ofpixels is as a unit for polarity inversion, as shown in an LCD panel 404of FIG. 4C, and the corresponding driving method is referred to astwo-column inversion.

FIG. 4D illustrates the dot inversion driving method for an LCD panel406 having a number of pixels, viewed as a number of dots. In dotinversion, the polarity of voltage applied to one pixel is the inverseof that applied to the pixels that surround the one pixel. That is, forone pixel that a negative voltage is applied to, voltages in positivepolarity are to be supplied to the pixels adjacent to the one on allsides (left, right, top, and bottom sides). In the next time instant,the polarities for every dot are changed.

For an LCD panel with a large size, such as panels used in notebookpersonal computers, a wide visual angle is achieved by formingmulti-domains in every single pixel of the panel. FIGS. 5A and 5Billustrate the arrangement of multi-domain liquid crystal molecules invertical alignment mode of an LCD panel when a voltage is applied or notapplied, respectively. For the sake of brevity, the arrangement of themolecules in a single pixel is described. As shown in FIG. 5A, when novoltage is applied, most of the liquid crystal molecules 500 are alignedvertically to a pixel electrode 502. The pixel electrode 502 has aprotrusion 504. The liquid crystal molecules adjacent to the protrusion504 are arranged substantially vertical to the protrusion 504, and havean inclination to the pixel electrode 502. In addition, the molecules onboth sides of the protrusion 504 incline to the both sides. When avoltage is applied, as shown in FIG. 5B, two different domain are formedon the single pixel because of the different inclinations of themolecules on the left and right sides of the protrusion 504. To be morespecific, the molecules adjacent to the left side of the protrusion 504affect the left portion of the liquid crystal molecules 500 of thepixel, so that the left portion of molecules incline to the left side.Likewise, the molecules adjacent to the right side of the protrusion 504affect the right portion of the liquid crystal molecules 500 of thepixel, resulting in the inclination of this portion of molecules to theright side. FIGS. 5A and 5B show the example with only two domains inone single pixel. However, multiple domains can be similarly implementedby changing the shape of the protrusion 504, leading to a wide visualangle.

As an example, in 1997, Fujitsu limited company produces a multi-domain,vertical alignment mode, thin film transistor (TFT) LCD panel having avisual angle of up to 160°. Since the liquid crystal molecules are invertical alignment mode, the panel has a contrast ratio of up to 300:1.However, the application of protrusions on the plate of the multi-domainpanel results in a reduction in its light efficiency.

Unlike LCD technology for use in large-sized panels, LCOS technology isapplied to small-sized panels, e.g., the liquid crystal panels for usein projectors or projection televisions. Besides, their LCOS panels arenot required to provide wide visual angles. Instead of relying on thepanel to provide wide visual angles, a projector with LCOS can employ anenhanced screen as a scattering surface to achieve wide visual angles.Accordingly, the consideration of wide visual angles in LCOS becomesunnecessary and the LCOS is only required to be capable of being struckby incident rays normal to the LCOS and of reflecting normal reflectedrays normal to the LCOS. Thus, the formation of one single-domain ineach pixel is sufficient. That is, in the present of an electric fieldfor the LCOS, the liquid crystal molecules in a pixel are inclined toone direction other than multi-directions as illustrated in FIG. 5B.

In brief, for meeting the requirements for the incident light andreflection of the reflected light normal to the LCOS panel, the liquidcrystal molecules in one single pixel are desired to be of single-domainand no protrusion, for the pixel, is formed on the plate of the LCOS. Inaddition, liquid crystal molecules in VA mode are chosen in order toprovide high contrast ratios. In the following, under different drivingmethods, the formation of the single-domain vertical alignment in a LCOSpanel and its reflection ratios corresponding to the twisted liquidcrystal molecules are illustrated, wherein four pixels are involved.Besides, the alignment films employ the rubbing process to cause theliquid crystal molecules to be arranged on the aligning files inparticular directions when no voltage is applied. When a sufficientvoltage is applied, the liquid crystal molecules incline to fixeddirections so as to form a single-domain in each pixel.

FIG. 6A illustrates a conventional VA mode LCOS when no voltage isapplied. Pixel electrodes 602, 604, 606, and 608 are formed on aninsulating layer 600, and grooves 610, 612, and 614 are formed among thepixel electrodes. FIG. 6B is a diagram of reflection ratio versuslocation on the liquid crystal layer corresponding to the four pixelsshown in FIG. 6A. Since no voltage is applied, most of the liquidcrystal molecules 616 are aligned and vertical to the pixel electrodes602 to 608, resulting in the LCOS having a reflection ratio of 0%.

FIG. 7A illustrates the LCOS in FIG. 6A driven by the frame inversiondriving method. Referring to FIG. 7B also, a diagram of reflection ratioversus location on the liquid crystal layer in FIG. 7A is shown. Inorder to display images with different brightness, LCD panels arecommonly required to produce different gray levels. Thus, voltages ofdifferent levels would be applied to adjacent pixels of the LCOS. Forinstance, the pixel electrodes 602 and 606 are supplied with a voltageof +3.6 V, while the pixel electrodes 604 and 608 with a voltage of +1.5V. Due to the voltages supplied, the liquid crystal molecules wouldtwist. As examined from FIG. 7A, the higher the voltages applied to thepixels, the larger the inclination angles of the liquid crystalmolecules 616. In addition, the dashed lines in FIG. 7A are indicativeof equipotential lines yielded after the voltages are applied to thepixel electrodes 602, 604, 606, and 608. By the pattern of theequipotential lines, the distribution of the electric field in theliquid crystal molecules can be determined. Since fringe field effectoccurs on the electric field near the edges of the pixel electrodes 602,604, 606, and 608, the potential lines near the edges of the pixelelectrodes 602, 604, 606, and 608 are distributed irregularly. Besides,because of a potential difference of 3.6−1.5 V=2.1 V between adjacentpixel electrodes, the distribution of the electric field near the edgesof the pixel electrodes becomes irregular, resulting in the liquidcrystal molecules 606 twisting in irregular directions. Thus, reflectionratios of two points a and b located near the edges of the pixelelectrodes 602, 604, 606, and 608 reduce to 0%. In other words, whilethe liquid crystal molecules, under the application of a voltage of +3.6V, are expected to provide a reflection ratio of about 40 to 50%, anundesired small gray area occurs on the right side of each of the pixelelectrodes 602 and 606, thus degrading the display quality of thepixels. Hence, for LCOS panel, the fringe field effect reduces thebrightness of the pixels and even produces black points.

FIG. 8A illustrates the LCOS in FIG. 6A driven by the two-columninversion driving method. Referring to FIG. 8B also, a diagram ofreflection ratio versus location on the liquid crystal layer in FIG. 8Ais shown. When the pixel electrodes 602 and 604 are supplied with avoltage of +3.6 V while the pixel electrodes 606 and 608 are suppliedwith a voltage of −3.6 V, the liquid crystal molecules 616, originallynormal to the pixel electrodes 602 to 608, are to be twisted. However,since the voltages applied to the adjacent pixel electrodes 604 and 606are in inverse polarities, an electric field in transverse directionoccurs between the two adjacent pixel electrode. That is, in theproximity of the groove 612, an electric field occurs in the directionfrom the pixel electrodes 604 to 606, in parallel to the X-axis.Besides, the fringe field effect of the electric field between the pixelelectrodes 604 and 606 on the electric field in the proximity of thegroove 612 causes the distribution of electric field to be irregular,resulting in the irregular inclinations of the liquid crystal moleculesnear the groove 612. Therefore, the reflection ratios, between the pixelelectrodes 604 and 608, that are expected to be 40% are now reduced to0%, such as that indicated by the point c.

FIG. 9A illustrates the LCOS in FIG. 6A driven by the dot inversiondriving method. Referring to FIG. 9B also, a diagram of reflection ratioversus location on the liquid crystal layer in FIG. 9A is shown. Thepixel electrodes 604 and 608 are supplied with a voltage of +3.6 V whilethe pixel electrodes 602 and 606 are supplied with a voltage of −3.6 V.Since the adjacent pixel electrodes 602 and 604 (604 and 606; 606 and608) are supplied with the voltages in inverse polarities, a transverseelectric field in the direction of X-axis occurs between the twoadjacent pixel electrodes. Besides, the fringe field effect of theelectric fields between the pixel electrodes 602, 604, 606, and 608causes the distribution of the electric fields in the proximity of thegrooves 610, 612, and 614, respectively, to be irregular. This resultsin the regular inclinations of the liquid crystal molecules 616 near theedges of the pixel electrodes 602 to 608. Hence, the reflection ratiosof the pixel electrodes 602, 604, 606, and 608 are reduced, and in theworst case, reflection ratios of zero occur on several points, such aspoints e, f, g, and h, as shown in FIG. 9B.

As can be examined from the performance of the above three drivingmethods (illustrated by FIGS. 6A–9B) for the conventional LCOS,irregular inclinations occur in the liquid crystal molecules near thepixel electrodes of the conventional LCOS because of the fringe fieldeffect of electric field produced by the pixel electrodes and the effectof transverse electric fields produced by adjacent pixel electrodessupplied with voltages in inverse polarities, e.g., in dot inversion.Thus, the reflection ratios in the regions of the pixels are reduced. Inthe worst case, black stripes would even occur in the pixel regions,degrading the display quality of the LCOS. Therefore, the loss of lighttransmission because of irregular molecule arrangement by the transverseelectric field and fringe field effect is a critical problem in thedevelopment of the single-domain vertical alignment mode LCOS desired tobe resolved.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a liquid crystalon silicon (LCOS) panel in single-domain vertical alignment mode. By aspecial configuration of protrusions and grooves among the pixels of theLCOS panel, a single domain is easily formed in every pixel while highcontrast ratio, reduced fringe field effect and effect of transverseelectric field can be achieved.

The invention achieves the above-identified object by providing an LCOSpanel in single-domain vertical alignment mode. The LCOS panel includesa front plate, a rear plate, and a liquid crystal layer. The rear plateincludes a number of pixel electrodes and the pixel electrodes aregrouped in pairs. Every two pairs of pixel electrodes are separated by agroove while the pixel electrodes in each pair are separated by aprotrusion. The LCOS panel is filled with the liquid crystal layer,between the front and rear plates, while the liquid crystal molecules inthe liquid crystal layer are in vertical alignment mode.

The invention employs liquid crystal molecules in vertical alignmentmode to increase the contrast ratio of the LCOS panel. In addition, inorder to form a single domain in every pixel, the invention uses astructure with protrusions and grooves to produce a pushing and pullingeffect on the liquid crystal molecules, causing the liquid crystalmolecules to incline rapidly to a specific direction. In this way, thestructure not only regulates the inclination of the liquid crystalmolecules, but also reduces fringe field effect and effect of transverseelectric field on the inclination of them.

Other objects, features, and advantages of the invention will becomeapparent from the following detailed description of the preferred butnon-limiting embodiments. The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a single pixel of reflective liquidcrystal on silicon panel.

FIG. 1B is a top view of the liquid crystal on silicon panel.

FIGS. 2A–2B show the operations of liquid crystal molecules in twistednematic mode when a voltage is not applied or applied, respectively.

FIGS. 3A–3B show the operations of liquid crystal molecules in verticalalignment mode when a voltage is not applied or applied, respectively.

FIG. 4A illustrates the conventional frame inversion driving method fora liquid crystal display (LCD) panel 400.

FIG. 4B illustrates the conventional column inversion driving method foran LCD panel 402.

FIG. 4C illustrates the conventional two-column inversion driving methodfor an LCD panel 404.

FIG. 4D illustrates the dot inversion driving method for an LCD panel406.

FIGS. 5A and 5B illustrate the arrangement of multi-domain liquidcrystal molecules in vertical alignment mode of an LCD panel when avoltage is applied or not applied, respectively.

FIG. 6A illustrates a conventional VA mode LCOS when no voltage isapplied to a liquid crystal layer of the LCOS.

FIG. 6B is a diagram of reflection ratio versus location on the liquidcrystal layer shown in FIG. 6A.

FIG. 7A illustrates the LCOS in FIG. 6A driven by the frame inversiondriving method.

FIG. 7B is a diagram of reflection ratio versus location on the liquidcrystal layer in FIG. 7A.

FIG. 8A illustrates the LCOS in FIG. 6A driven by the two-columninversion driving method.

FIG. 8B is a diagram of reflection ratio versus location on the liquidcrystal layer in FIG. 8A.

FIG. 9A illustrates the LCOS in FIG. 6A driven by the dot inversiondriving method.

FIG. 9B is a diagram of reflection ratio versus location on the liquidcrystal layer in FIG. 9A.

FIGS. 10A, 10C, and 10D are top views of the arrangement of pixels of anLCOS according to a first embodiment of the invention.

FIG. 10B is a cross-sectional view taken along line AA′ shown in FIG.11A.

FIG. 11A illustrates the LCOS according to the first embodimentillustrated in FIGS. 10A and 10B when no voltage is applied to a liquidcrystal layer of the LCOS.

FIG. 11B is a diagram of reflection ratio versus location on the liquidcrystal layer shown in FIG. 11A.

FIG. 12A illustrates the LCOS shown in FIG. 11A driven by the frameinversion driving method.

FIG. 12B is a diagram of reflection ratio versus location on the liquidcrystal layer shown in FIG. 12A.

FIG. 13A illustrates the LCOS shown in FIG. 11A driven by the two-columninversion driving method.

FIG. 13B is a diagram of reflection ratio versus location on the liquidcrystal layer shown in FIG. 12A.

FIG. 14A illustrates the LCOS shown in FIG. 11A driven by the dotinversion driving method.

FIG. 14B is a diagram of reflection ratio versus location on the liquidcrystal layer shown in FIG. 14A.

FIG. 15A is a top view of an LCOS according to a second embodiment ofthe invention.

FIG. 15B is a top view of an LCOS according to a third embodiment of theinvention.

FIGS. 16A–16C illustrate various protrusions and grooves according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

The technical feature of the invention is the application of a structurewith protrusions and grooves to a liquid crystal on silicon (LCOS)panel, wherein the pixel electrodes of the LCOS are grouped in pairs,every two pairs of the pixel electrodes are separated by a groove, andthe pixel electrodes of each pair of the pixel electrodes are separatedby a protrusion. By the structure with protrusions and grooves,single-domain liquid crystal molecules in vertical alignment (VA) modecan be formed smoothly, and the fringe field effect and the effect ofthe transverse electric field are reduced.

FIG. 10A illustrates the arrangement of the pixels of an LCOS accordingto a first embodiment of the invention, wherein nine pairs of pixelelectrodes are representative of the pixel electrodes of the LCOS. Thepixel electrodes of the LCOS, such as pixel electrodes 1001, 1002, 1003,1004, and 1005, are grouped in pairs, such as pixel electrode pairs 1020and 1022. Every two pairs of the pixel electrodes are separated by agroove, such as grooves 1013 and 1018. The pixel electrodes of each pairof pixel electrodes are separated by a protrusion, such as protrusion1015.

FIG. 10B is a cross-sectional view taken along line AA′, illustratingthe effect of the protrusion 1015 and the groove 1018 on the liquidcrystal molecules. In FIG. 10B, the pixel electrodes 1001, 1002, and1003 are formed separately on an insulating layer 1000. The pixelelectrodes 1002 and 1003 are paired and separated by the protrusion1015, while the pixel electrode 1002 is separated from another pixelelectrode 1001 by the groove 1018. The protrusion 1015 is higher thanthe pixel electrode 1002 as well as the pixel electrode 1003 while thedepth of the groove 1018 can be equal to the height of either of thepixel electrodes 1001 and 1002. In addition, the cross-section of theprotrusion 1015 is similar to a triangle, and the protrusion 1015 has aleft side 1014 and a right side 1016. The groove 1018 has a left incline1019 and a right incline 1017. The pixel electrodes 1001, 1002, and 1003are covered by a number of reflection layers (not shown), respectively.Besides, an alignment film (not shown) covers the pixel electrodes 1001,1002, 1003, the protrusion 1015, and the groove 1018. Affected by thealignment film, the liquid crystal molecules 1010, 1008, and 1012, as novoltage is applied to them, are arranged vertically on the right incline1017 of the groove 1018, the upper surface of the pixel electrode 1002,and the left side 1014 of the protrusion 1015, respectively.

Moreover, when no voltage is applied, the liquid crystal molecule 1010is located on the right incline 1017 of the groove 1018, inclining tothe Y-direction at a first inclination angle while the liquid crystalmolecule 1012 is located on the left side 1014 of the protrusion 1015,inclining to the Y-direction at a second inclination angle. Theinclination of the liquid crystal molecule 1012 produces a push on theliquid crystal molecule 1010 to the Y-direction and the inclination ofthe liquid crystal molecule 1012 produces a pull on the liquid crystalmolecule 1018 to the Y-direction. By the effect of the push and pull,when a voltage is applied to the pixel electrode 1002, the liquidcrystal molecules over the pixel electrode 1002 are to be inclined tothe Y-direction, forming single domain for the LCOS. Because of thestructure with the protrusion 1015 and groove 1018, the formation ofsingle domains can be effectively achieved. Therefore, in the invention,it is unnecessary for the alignment film to use rubbing process tocontrol the inclination of the liquid crystal molecules when voltagesare applied.

Likewise, the liquid crystal molecules (not shown) on the right side ofthe protrusion 1015 incline to the Y-direction. When a voltage isapplied to the pixel electrode 1003, liquid crystal molecules over thepixel electrode 1003 will incline to the Y-direction, forming a singledomain.

The formation of the protrusion 1015 between the pixel electrodes 1002and 1003 is advantageous to the reduction in the effects of the fringefield and transverse field between the pixel electrodes 1002 and 1003,resulting in enhanced uniformity of the arrangement of the liquidcrystal molecules between the pixel electrodes 1002 and 1003. By theinvention, the problem of irregular reduction in reflection ratio andthe production of black stripes in the pixel regions for theconventional liquid crystal on silicon panels can be effectivelyresolved and the display quality can be thus enhanced.

In FIG. 10A, two adjacent pixel-electrode pairs disposed in thetransverse direction are separated by a groove. Similarly, two adjacentpixel-electrode pairs disposed in the vertical direction, e.g., thepixel-electrode pairs 1020 and 1022, are separated by a groove, e.g.,groove 1024. The protrusion 1026 of the pixel-electrode pair 1020 isseparated from the protrusion 1028 of the pixel-electrode pair 1022 bythe groove 1024, also. The edges of the protrusions 1026 and 1028 nearthe groove 1024 can be clean edges. Besides, they can be outward edgesas shown in FIG. 10C; or can be inward edges as shown in FIG. 10D.

Moreover, according to the invention, the LCOS panel uses a glasssubstrate (not shown) with no pattern for the pixel electrodes. In thisway, in the manufacturing process for an LCOS panel of the invention,the position of its front and rear plates can be readily to beregulated, thus enhancing the yield of the panel. The front and rearplates are spaced apart for a cell gap H.

In the following, the LCOS panel according to the invention is driven bydifferent driving methods. The arrangements of its liquid crystalmolecules and the corresponding reflection ratios are illustrated.

FIG. 11A illustrates the arrangement of the liquid crystal molecules ofa LCOS panel in vertical alignment mode according to a first embodimentwhen no voltage is applied. Referring to FIG. 11B also, it shows adiagram of reflection ratio versus location on a liquid crystal layer1102. The arrangement of the liquid crystal molecules of the liquidcrystal layer 1102 is determined by the potential differences betweenthe a transparent electrode 1100, the pixel electrodes 1001, 1002, 1003,and 1004, and the direction of the electric field induced between them.When no voltage is applied, the LCOS panel has a reflection ratio of 0%,substantially.

FIG. 12A illustrates the LCOS panel in FIG. 11A driven by frameinversion. FIG. 12B shows a diagram of reflection ratio versus locationon the liquid crystal layer in FIG. 12A. The pixel electrodes 1001 and1003 are supplied with a voltage of +3.6 V while the pixel electrodes1002 and 1004 are supplied with a voltage of +1.5 V. As shown in FIG.12A, when voltages are applied, the liquid crystal molecules twist indifferent angles corresponding to the supply voltages of differentvalues, so as to provide different reflection ratios. Affected by theprotrusion 1015 and the groove 1018, the liquid crystal molecules overthe pixel electrode 1002 incline to the Y-direction while the liquidcrystal molecules over the pixel electrode 1001 incline to the inverseof Y-direction. In the proximity of the groove 1018, because the liquidcrystal molecules between the pixel electrodes 1001 and 1002 aresqueezed by the liquid crystal molecules that incline to differentdirections on both sides of the groove 1018, they are arranged in thedirection approximately vertical to the Y-direction, and have areflection ratio of 0%. As shown in FIG. 12B, over the pixel electrodes1001 and 1003, the reflection ratio maintains at about 25% and no grayregion as shown in FIGS. 7A and 7B occurs.

FIG. 13A illustrates the LCOS panel in FIG. 11A driven by two-columninversion. FIG. 13B shows a diagram of reflection ratio versus locationon the liquid crystal layer in FIG. 13A. The pixel electrodes 1003 and1004 are supplied with a voltage of −3.6 V while the pixel electrodes1002 and 1005 are supplied with a voltage of +3.6 V. On either side ofthe groove 1013, since the pixel electrodes 1003 and 1004 are in thesame polarity, the fringe field effect and transverse field effect areinsignificant and do not degrade the display quality of thecorresponding pixels. On either side of the protrusion 1015, the pixelelectrodes 1002 and 1003 are in the opposite polarities, a transversefield is present between the two pixel electrodes. However, since theprotrusion 1015 produces a force much larger than the force produced bythe transverse field, the liquid crystal molecules maintains in regulararrangement. Therefore, the liquid crystal molecules near the protrusion1015 will not twist irregularly as that in the conventional approaches,thus avoiding the display quality from being degraded. As compared withthe LCOS indicated by FIGS. 8A and 8B, the LCOS indicated by FIGS. 13Aand 13B provides a better display quality and has only having 0%reflection ratio at points i and j. Although the points i and j areindicative of reflection ratios of 0%, since their locations areassociated with the protrusions 1015 and 1025, which are opaque regions,the display quality of the whole LCOS are not degraded.

FIG. 14A illustrates the LCOS panel in FIG. 11A driven by dot inversion.FIG. 14B shows a diagram of reflection ratio versus location on theliquid crystal layer in FIG. 14A. The pixel electrodes 1003 and 1005 aresupplied with a voltage of −3.6 V while the pixel electrodes 1002 and1004 are supplied with a voltage of +3.6 V. On either side of the groove1013, since the pixel electrodes 1003 and 1004 are supplied withvoltages in opposite polarities, a transverse field is produced. Thus,it results in the liquid crystal molecules near the groove 1013 arrangedirregularly and gray points, such as a point k, are displayed. In thisexample, when the pixel electrodes are supplied with the voltages inopposite polarities, the effect of the transverse field produced isunable to be avoided. However, as compared with the display qualitypresented by the LCOS in FIGS. 9A and 9B, the display quality presentedby the LCOS in FIGS. 13A and 13B is better. In addition, when the slopesof the two inclines of the groove are reduced, the aperture of thegroove becomes larger, allowing further improvement of the displayquality.

As examined from the three driving methods (illustrated in FIGS.11A–14B), it shows that the structure which has protrusions and groovesother than using rubbing process and the way which makes the liquidcrystal molecules arranged in one single direction in one single pixelcan effectively reduce the fringe field effect as well as the transversefield effect and enhance the display quality of the single domainvertical alignment mode LCOS. Among the three driving methods, the frameinversion and two-column inversion can be used to drive the verticalalignment mode LCOS according to the invention, obtaining better displayquality.

Moreover, the results presented by FIGS. 11A–14B provides a reason whythe protrusions are not suitable to be substitute for the grooves. Iftwo protrusions are disposed on either sides of a pixel electrode,pushes from the two sides will exert on the liquid crystal moleculesover the pixel electrode, resulting in the liquid crystal molecules inthe middle of the pixel electrode to be twisted to normal or anundesired direction even in the presence of an electric field.Accordingly, a black stripe will be formed in the middle of the pixelelectrode so that black points are displayed on the LCOS.

In theory, the heights of the protrusions are expected to be as higheras possible. The higher the protrusions the larger the pushes on theliquid crystal molecules. In the invention, the heights of protrusionscan be at least ⅕ of cell gap H, and, preferably, ⅓ of cell gap H.However, the yield of the LCOS reduces as the protrusions become higher.In addition to the size and shape of the protrusions, the electric fieldnear the protrusions can be affected by the material for theprotrusions. When a voltage is applied to the LCOS, the pushes of theliquid crystal molecules near the protrusions with low dielectricconstant are larger. Thus, materials for the protrusions are preferablyto be low dielectric constant materials, e.g., silicon dioxide with adielectric constant of 3.9, or other material having a dielectricconstant approximate to 3.9. In general, a good performance can beobtained by using materials of a dielectric constant of 10 to form theprotrusions.

Further, the pixel electrodes on the LCOS can be paired in a way otherthan that illustrated in FIG. 10A. FIG. 15A shows an LCOS according to asecond embodiment of the invention in a top view. The LCOS has a numberof pairs of pixel electrodes, protrusions, and grooves. For the pairs ofpixel electrodes, such as the pixel-electrode pair 1502, the protrusionsbetween and the grooves near the pairs of pixel electrodes, such as theprotrusion 1504 and the groove 1506, are arranged alternately so that,as viewed along the rows and columns of the protrusions of the LCOS,there is one groove between two adjacent protrusions, and as viewedalong the rows and columns of the grooves of the LCOS, there is oneprotrusion between two adjacent grooves. Referring to FIG. 15B, a topview of an LCOS is shown according to a third embodiment of theinvention, wherein its pixel electrodes are arranged in a diamond form.As shown in FIG. 15B, the structure with protrusions and grooves of theinvention can be applied to the pixel electrodes 1508 arranged in thediamond form. The arrangement of the pixel electrodes in a diamond formcan be applied to projection televisions so as to provide an enhanceddisplay quality.

As described above, the structure with protrusions and grooves doeseffectively reduce the fringe field effect and transverse field effectoccurred in an LCOS. Moreover, the protrusions and grooves can bedesigned in different sizes and shapes. The structures with protrusionsand grooves with different shapes are illustrated in FIGS. 16A to 16C. Agroove 1602 can be formed with two inclines at different slopes, asshown in FIG. 16A. In FIG. 16B, a protrusion 1604 can be further coveredwith pixel electrodes 1606 and 1608. In FIG. 16C, the depth of a groove1610 can be larger than the thickness of a pixel electrode 1612. Forobtaining a deeper groove such as the groove 1610 shown in FIG. 16C, aportion of an insulating layer 1614 can be etched by using amanufacturing process with yellow light. Certainly, the inclines of thegroove 1610 can be steeper, e.g., with an inclination of 70°. In brief,any structure with protrusions and grooves that produces a single domainof the liquid crystal molecules for a pixel so that the single domainsproduced on two sides of the protrusions are in different directions isunder the scope of the invention.

While the invention has been described by way of example and in terms ofa preferred embodiment, it is to be understood that the invention is notlimited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

1. A liquid crystal panel, comprising: a front plate; a rear plateincluding a plurality of pixel electrodes, wherein every two pixelelectrodes are paired as a pixel electrode group, every two pixelelectrode groups are separated by a groove, and the pixel electrodes ofeach pixel electrode group are separated by a protrusion; and a liquidcrystal layer, with which the space between the front plate and rearplate is filled, wherein the liquid crystal layer has liquid crystalmolecules in vertical alignment mode.
 2. The liquid crystal panelaccording to claim 1, wherein the protrusion is made of dielectricmaterial of low dielectric constant.
 3. The liquid crystal panelaccording to claim 1, wherein the protrusion has a dielectric constantof smaller than
 10. 4. The liquid crystal panel according to claim 2,wherein the protrusion is made of silicon dioxide.
 5. The liquid crystalpanel according to claim 1, wherein the front plate and the second plateare apart in a cell gap and the protrusion has a height of at least onefifth of the cell gap.
 6. The liquid crystal panel according to claim 1,wherein the groove has a first inclination and a second inclination, andthe first inclination is opposite to the second inclination.
 7. Theliquid crystal panel according to claim 1, wherein the protrusions andthe grooves are arranged alternately.
 8. The liquid crystal panelaccording to claim 1, wherein the groove has a depth equal to that ofthe pixel electrodes.
 9. The liquid crystal panel according to claim 1,wherein the rear plate further comprises an insulating layer, the pixelelectrodes are disposed above the insulating layer, and the groove has adepth larger than that of the pixel electrodes.
 10. A liquid, crystalpanel, comprising: a front plate; a rear plate including a plurality ofgroups, each group having two pixel electrodes and a protrusiontherebetween, wherein the groups are separated from each other byrespective grooves; and a liguid crystal layer, with which the spacebetween the front plate and rear plate is filled, wherein the liguidcrystal layer has liguid crystal molecules in vertical alignment mode:wherein the protrusion is made of dielectric material of low dielectricconstant; and wherein the protrusion is made of silicon dioxide.
 11. Theliquid crystal panel according to claim 10, wherein the protrusion has adielectric constant smaller than
 10. 12. The liquid crystal panelaccording to claim 10, wherein the front plate and the rear plate areapart in a cell gap and the protrusion has a height of at least onefifth of the cell gap.
 13. The liquid crystal panel according to claim10, wherein the protrusions and the grooves are arranged alternately.14. The liquid crystal panel according to claim 10, wherein the groovehas a depth equal to that of the pixel electrodes.
 15. The liquidcrystal panel according to claim 10, wherein the rear plate furthercomprises an insulating layer, the pixel electrodes are disposed abovethe insulating layer, and the groove has a depth larger than that of thepixel electrodes.
 16. A liquid crystal panel, comprising: a front plate;a rear plate including a plurality of groups, each group having twopixel electrodes and a protrusion therebetween, wherein the groups areseparated from each other by respective grooves; and a liguid crystallayer, with which the space between the front plate and rear plate isfilled, wherein the liquid crystal layer has liquid crystal molecules invertical alignment mode; wherein the groove has a first inclination anda second inclination, and the first inclination is opposite to thesecond inclination.